Two-point modulation technique is widely used in telecommunications and avoids an issue of limited bandwidth of a phase-locked loop (PLL) by an approach of splitting the modulating data into two parts: one is transmitted to the voltage-controlled oscillator (VCO), and the other one is to the delta-sigma modulator (SDM). However, a two-point modulator requires a digital to analog converter (DAC) and/or other circuits at the input of the VCO to convert the modulating data into an analog form, and hence the power consumption of the device is increased. Moreover, the gain mismatching between two modulation paths causing signal distortion is another issue.
Therefore, there is a need to provide a simple, low power, low cost and self-calibration modulation circuit and operating method thereof.